US1613335A - Ammonium-nitrate explosive - Google Patents

Description

Jan. 4,1927., 1,613,335

E. M. SYMMES AMMONIUM NI TRATE EXPLOS IVE Filed N'ov. 8, 1924 Patented Jan. `4, 1927.

UNITED STATES A 1,613,335 PATENT OFFICE.

ERNEST M. SYMMES, OEWILMINGTON, DELAWARE, ASSIGNOR TO HERCULES POWDER COMPANY,.OF WILMINGTON, DELAWARE, A CORPORATION 0F DELAWARE.

ANTIMONIUM-NITRATE EXPLOSIVE.

The object of myinvention is to provide an ammonium nitrate explosive which is distinguished from ordinary ammonium' nitrate explosives in`that it is less hygroscopic, more sensitive, much less dense, thus allowing a higher cartridge count, and which, as it passes through the transition Apoint at 32 C., will n0t,,set up (harden) and so become so relatively insensitive that it may not 'detonate properly.

The manufacture of my improved explosive is dependent on the use of ammonium nitrate having peculiar novel physical characteristics, and in order to properly describe tlie production o'f explosives embodying this invention, it is necessary to describe the improved ammonium nitrate which is a constituent of the explosive and the method of making it.

In the ordinary process of making ammonium nitrate, it is customary to prepare weak solutions of the salt and evaporate the solution to a certain concentration at a certain temperature,l after which the solution is discharged into a gra'ining kettle and slowly crystallized with agitation and cooling at a certain rate. The rate of crystallization and concentration of the evaporated solution controls the fineness of the product. Slow crystallization of a highly concentratedlsolution produces coarse particles in the form of irregular botryoidal solid crystals., Crystallizing at an increased rate results in relatively fine particles, which are also in the form of solid crystals.

Granular ammonium nitrate produced by this process is composed of solid grains, has greater density and hygroscopicity than is desirable, and when passing through the transition point at 32 C. (89.6 F.) there is considerable external expansion, which constitutes a serious objection to explosives containinrT ammonium nitrate 11i substantial proportion, as the explosive sets (hardens) r as it passes through the transition point and becomes relatively insensitive and may not vdetonate properly. y

The granular ammonium nitrate embodying the present invention is superior to the productformed by'crystallizing a more or less concentrated solution in a graining kettle. As compared with the ordinary product` it is milch less dense, thus allowing a higher cartridge count in ammonium'nitrate permissible explosives; it is more sensitive; it is less hygroscopic; and in ypassing `through the transition point at 32 C., there 1s less external expansion and it therefore does not exhibit such a marked tendency to set up. i

It is certain thatsome of the above qualities, and it is possible that all of them, ai'e due, in whole or in part, to the peculiar novel physical characteristic exhibited by the granular ammonium nitrate embodying the present invention: namely, the granules or particles are substantially spherical inl form and have a hollow center. Such hollow spherical paiticles cannot be manufactured by the process in general use: namely, the crystallization in graining kettles with .agitation and cooling. On the other hand, their formation is not necessarily dependent on the use of any particular process and is certainly not dependent on the use of any particular apparatus. i In order, however, that my improved product may be produced by those skilled in the art, I shall describe a process of making it which has been found entirely satisfactory as Well as operative. This process is set forth in a companion application liled of even date herewith, Serial Number 748,548. Itcomprises the projection of an evaporated solution of ammonium nitrate, through a nozzle or atomizer, at a substantially definite pressure, into a gaseous cooling medium. An apparatus adapted to carry out the process is shown in the accompanying drawing, which is a longitudinal sectional view of such apparatus.

A weak neutral ammonium nitrate liquor is concentrated in the evaporator a. From the evaporator the more or less concentrated solution, by means of a pump 7), is conveyed through a steam-jacketed pipe c and discharged through a nozzlel (l into the spray chamber e under suliioient pressure to elfcct the atomization of the solution. VIt should be understood that the term atoniization is used in its popular sense to imply a division ofthe solution into a number of very line particles, which will solidify' before they have traversedthe height of the spray chainber. The spray chamber is of substantial dimensions and is provided wili a sloping bottom communicating with a hopper f which discharges the material into a rot-ating drying cylinder. g. From the drying cylinder the dried material ,is discharged, say, onto a screen l1.; the grams which 1t 1s desired to utilize. as an explosive ingredient passing through the screen in to a receiver z', while the tailings pass over into a separate receiver By means of a heater and a blower m, a current of hot air or other gas is forced through thedrier, the air thence escaping through the hopper f into the spray chamber e.

The character of the material produced by the improved process is controlled by the conditions under which the process is carried out. It has been found that the density of the material varies in asubstantially direct ratio to the freezing point, of the solution sprayed and in a substantially inverse ratio to the temperature of the solution and degree of atomization. In other words, the density of the product resulting from spraying a solution having a freezing polnt only slightly below the temperature of the solution when sprayed will be higher than that of the product from a solutionhaving the same freezing point but sprayed at a higher temperature. By controlling the freezin point and temperature of the solution an the degree of atomization, the character of the product'may be controlled. The freezing point of the solution varies with the degree of concentration. The degree of atomization may be varied by varymg the pressure at the nozzle and to some extent by varying the temperature of the solution when sprayed.

As an illustrationof the process, a weak solution of ammonium nitrate is concentrated in the evaporator a to a point where the solution has a temperature of 310 F.

and at which the ammonium nitrate if taken out would freeze or erystallize at 280 F. With a steam pressure of fifty pounds to the square inch on the jacketed feed pipe c, thev solution is delivered through the pump to the nozzle d at a pressure of twenty pounds to the square inch.

The heated air in chamber f may be at any desired temperature (say 100 F. to 150 F and is substantially devoid of moisture. 'Ihis air, however, is very cold relatively to the incoming spray of ammonium nitrate, and almost immediately cools the sprayed particles to the point of solidicaton. It will be understood that there is a continuous current of dry air flowing into the bottom of chamber e and out the ventilators o at the lop thereof.

The ammonium nitrate is projected in the form of a vast number of particles of spherical form. From contact with the cooling gaseous medium filling the spray chamber, these spheres quickly form an exterior solidified shell. The interior of each particle .freezes more slowly and, due to the contraction that takes place on cooling, a void space is left in the interior. The product has an apparent density of about .70 andv a ineness (with the freezing point, temperature and degree of atomization specified as an example) such that ninety-five per cent will pass through a ten mesh screen and be held on a forty mesh screen. By increasing the atomizing action, finer particles are produced. For example, the degree of fineness may be such that not more than five per cent will be held on a forty mesh "screen, while five per cent or more will pass through a hundred mesh screen, Whatever the degree of fineness, the grains have a spherical form with an interior void space. Besides being muchless dense than granular ammonium nitrate produced by the ordinary method, they are less hygroscopic and show less increase in volume when passing through the 32 C. transition point.

The size and density of the material are both affected by, and may be controlled by regulating, the freezing point, temperature and degree of atomization of the liquid when sprayed. In all cases, however, the density will be low as compared with the ordinary product and there will be a close approximation to uniformity in size. The density can be easily varied from .6 to .9.

While the weak solution is described as being concentrated to a point where the solution has a temperature of 310 F., crystallizing at 280 F., it is contemplated that these temperatures shall be subject to variation, dependent on the character or qualityl that it is desired to impart to the' ultimate product. It is impracticable, however, 'to carry either the crystallizlng temperature or the evaporating temperature much higher than 310 F., as decbmposition occurs in the neighborhood of 320 F. The lowest practicable crystallizing temperature would be 250 F. or higher. The temperature of the gas entering the spray chamber is imma- -terial so long as it is substantially below the temperature of the liquid as it ,is being atomized. The gas should, of course, be nearly free from moisture. All required conditions can be .satisfied by using air as the gaseous cooling medium and heating it to above 100 F. and below 150 F. I

The following are examples of ammonia permissible explosives embodying my invention, bearing in mind that the ammonium nitrate ingredient has the peculiar characteristics and qualities hereinbcfore descril'ied.

An anun'onia permissible explosive having the followmg typlcal compositiom,

Percent. Nitroglycerin, nitropolyglycerin, nitrosugar, mtroglycol, or any other similar liquid explosive. y 10 Carbonaceous material 10 Ammonium nitrate 80 Nitroaromatic compounds 3 Sodium nitrate 41 Carbonaceous material 11 Ammonium nitrate 28 Ammonia gelatin (the example given being low freezing) Per cem.. Any of the above speciiedliquid explosives Nitrocotton 0.6 Sodium nitrate 46.4 Sulphur 3.0 Carbonaceous material 15.0 Ammonium nitrate 6.0

Having now' fully described my invention, what I claim and desire to protect by Letters Patent is:

1. An explosive composition comprising a liquid explosive, carbonaceous material and ammonium nitrate in the form of a multitude of substantially spherical grains with internal cavities.

2. An explosive composition comprising a liquid explosive, carbonaceous material and ammonium nitrate in the form of hollow granules having a density between .6 and .9.

3. An explosive composition comprising a liquid explosive, carbonace `us material and ammonium nitrate in the form of granules having an internal void space and having, as compared with ordinary commercial ammonium nitrate, substantially lower density and less hygroscopicit and which Will not substantially set or har en in passing through the transition point at 32 C.

In testimony of which invention, I have hereunto set my hand, at Wilmington, Del., on this 5th day of November, 1924.

ERNEST M. SYMMES.

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